This invention relates to dispersion aids for polymers; more particularly this invention relates to dispersion aids for polymers made from polymer salts of low molecular weight, copolymers of alpha-olefins and alpha, beta-ethylenically unsaturated carboxylic acid.
It is known in the art to use ionic copolymer additives in various polymers to improve properties. The ionic copolymers disclosed in the art are made from copolymers of alpha-olefins and alpha,beta-ethylenically unsaturated carboxylic acid. However, these copolymers are generally of higher molecular weights and are used to improve polymer properties unrelated to processing and improved pigment dispersion such as impact resistance. Examples of these are U.S. Pat. Nos. 3,264,272 and 3,404,134, 3,347,957 and 4,210,579. The high molecular weight of the copolymer acids used to make the ionic copolymers are reflected by the fact that these higher molecular weight copolymers have measurable melt indexes, and that they can be processed by milling.
Low molecular weight copolymer salts are disclosed in U.S. Ser. No. 219,144 filed Dec. 22, 1980, now abandoned. These salts have been found to be useful as polymer lubricants in U.S. Ser. No. 222,197 filed Jan. 2, 1981, now U.S. Pat. No. 4,412,040. Low molecular polyethylene homopolymers have been used as disperson aids in polymers in which they are compatible. However, low molecular weight homopolymers can not be used as dispersion aids in nylon, polystyrene, polycarbonates, polyester due to incompatibility.